As dry developing processes in various electrostatic copying systems practically used at present, there are a one-component developing system using a toner containing a magnetic substance in the inside of the toner and a two-component developing system using a toner and a carrier such as an iron powder, etc.
In the case of the one-component developing system using a magnetic toner, since an automatic concentration controlling apparatus, etc., which are used for the developing machine of the two-component developing system are not required, the apparatus becomes compact and also since there is no stain with a carrier, a maintenance such as a carrier exchange is not required. Therefore, the one-component developing system has been used not only for small-sized copying machines and printers of a low speed but also for copying machines, printers, and plotters of an intermediate speed or higher and the further improvement of the performance thereof has been expected.
Recently, a digital system has been developed not only for a printer but also for a copying machine, it becomes possible to form latent images more high precisely and to express a delicate gradation by small characters and dots. In particular, a more small-sized apparatus utilizing the one-component developing system has been developed on a plotter for large-sized drawings and it has become possible to more faithfully and decisively reproduce the thickness of the lines of the drawings by a digital system to form high-precise latent images. However, the technique of obtaining images of a high image quality by developing the high-precise latent images thus formed has not yet been sufficiently realized.
As described above, the one-component developing system has various excellent features but has problems to be solved for achieving the high-image quality development. That is, there are problems that the toners are aggregated by the magnetic substance contained in the inside of the toners at development to make coarse the toner, whereby it becomes difficult to faithfully develop latent images, and the fine powder of the unfixed magnetic substance forms from the magnetic toner.
On the other hand, since the two-component developing system has a feature of being easily controlled, etc., because the carrier takes charge of the functions of stirring, transporting, charging, etc., of the developer and in the system, the function as the developer is separated, the two-component developing system has been widely used at present and, in particular, a developer using the carriers coated with a resin is excellent in the charge controlling property and in the case of using the developer, the improvements of the environmental reliance and the stability with the passage of time are relatively easy.
However, with the increase of the demand for small-sizing of the apparatus and energy saving, a toner which can be fixed with a lower energy has been required and for the purpose, a polyolefin wax is added to the one-component magnetic toner and the two-component non-magnetic toner. By the addition of the polyolefin wax, the occurrence of an offset phenomenon that when the toner is applied for a heat roll fixing method, the toner sticks to the heat rolls to stain the successive copies, is prevented, the occurrence of a smudging phenomenon that when after fixing the toner, the toner images formed are rubbed with a white paper, a part of the toner images is broken and transferred onto the white paper, is prevented, and further, the formation of a finger mark which is the phenomenon of destroying the fixed toner images with a finger for releasing the paper after passing the heat rolls is also prevented, thereby the fixing property is improved.
However, although the polyolefin wax-added toner shows a good releasing property from the heat rolls and shows good anti-offset property, there is a fault that polyolefin forms large domains in the resin since the compatibility of polyolefin with a binder resin is low. Thus, the toner is ground at the domain portions at the preparation of the toner, and the wax is liable to expose on the surface of the toner. Also, when the sizes of the toner are reduced for realizing high-quality images, the amount of the wax on the surface of the toner is more increased.
When latent images are developed using such a toner, the wax is transferred onto the developing sleeve and the photoreceptor to cause uneven toner transferring and stains of the photoreceptor, whereby lowering of the density and the deterioration of images occur.
For removing such troubles by the wax, a toner wherein the amount of the wax on the surface of the toner is defined is proposed as described in JP-A-2-87159 (the term "JP-A" as used therein means an "unexamined published Japanese patent application"). However, the toner thus prepared has a problem that the toner is yet insufficient for preventing the occurrences of lowering of the anti-offset property, lowering of the fixing property, etc.
Also, a toner containing two kinds of inorganic fine powders each defined by the molecule weight thereof and the BET surface area is proposed as described in JP-A-6-89044. However, since in the toner, the domains formed by the wax are large and the exposed amount of the wax is large, the toner has a problem that it is difficult to completely restrain the occurrence of filming by the wax although the toner has a polishing effect with the inorganic fine powders.